In recent years, the soft drink industry has adopted an internally threaded thermoplastic closure for application to the threaded necks of soft drink beverage bottles. Typical closures of this type are shown in U.S. Pat. Nos. 3,987,921 and 4,016,996.
This event has created a massive market for such closures which can only be economically produced in large quantities by injection molding in multi-cavity injection molds. However, due to the relatively complicated interior construction of such closures, involving both internally projecting threads in the side wall and a sloped annular sealing rib on the inner side of the panel of the closure, it is necessary that the closure be stripped from the core pin of the forming mold and this, in turn, requires that the molded article be cooled to essentially a self-sustaining temperature before the stripping action can occur. Therefore, there is a distinct need to apply improved cooling to the mold producing such articles in order to effect a significant reduction in the cycle time, hence in the number of articles produced per hour by a given injection molding machine.